Machining apparatus and machining method

ABSTRACT

A machining device ( 6 ) for machining a workpiece by relatively rotating the workpiece and a tool ( 1 ) which comprises a revolving shaft ( 8 ) held for rotation on its own axis that is parallel with the center axis, a main shaft ( 4 ) that is eccentric with respect to the center axis of the revolving shaft ( 8 ) and that rotates on its own axis that is parallel with the center axis of the revolving shaft ( 8 ), the main shaft having either the workpiece or the tool ( 1 ) mounted on the front end thereof, and rotation drive mechanisms (M 1 , M 3 ) for rotating the revolving shaft ( 8 ) and main shaft ( 4 ) at different rpm&#39;s.

TECHNICAL FIELED

The present invention relates to a machining apparatus and a machiningmethod for machining a workpiece by rotating a tool and the workpiecerelatively and, more particularly, to an apparatus and a method forrotating and revolving either the tool or the workpiece.

BACKGROUND ART

In a so-called contouring operation or a machining operation, a cuttingtool having a cutting blade is revolved around a work material(workpiece) while the cutting tool is rotated on its own axis. Thismachining method is typically exemplified by an end milling operation,an example of which is described in Japanese Patent Laid-Open No.63-212442 (JP-A-63-212442). According to the contouring method describedin this publication, before the workpiece is machined by rotating andrevolving an end mill, a turning diameter of an edge of the rotating andrevolving end mill is measured with a laser beam, and a tool diameter ofthe end mill is compensated by means of tool diameter compensationfunction of a numerical control unit on the basis of the result of theaforementioned measurement. In an actual cutting operation, on the otherhand, the end mill is at first inserted in the center of a bore to becut and moved therefrom to a position where the edge of the end millcontacts with the inner surface of the hole to be cut, morespecifically, to a position corresponding to a machining diameter, andthereafter moved along the inner face of the bore to be cut. In short,the end mill is revolved by rotating the end mill, as mounted on aspindle of a machine tool, on its own axis and by moving the spindle ina circular motion in a so-called X-Y plane.

In addition to the aforementioned apparatus, there is known an anothertype of apparatus using a mechanism of a polar coordinate system. Morespecifically, on a leading end of a main arm, which is rotated or givenan oscillatory rocking motion by a motor, there are mounted a motor forthe spindle and a tool shaft arm. On a leading end of the tool shaftarm, there is mounted a tool shaft which is rotated by the motor for thespindle. In this kind of apparatus, the tool shaft is moved in acircular motion, that is, revolved either by giving the main armassociated with the tool shaft arm a rocking motion or by rotating themain arm. Radius of revolution of the tool shaft are changed by varyingrelative angles of the tool shaft arm to the main arm.

There is known a still another type of apparatus which is constructedsuch that a tool shaft is so mounted on a first axis as to move in theradial direction thereof. This tool shaft is rotated with the firstaxis, resulting in the tool shaft revolving. The revolution radius ofthe tool shaft is changed by varying positions of the tool shaft in theradial direction of the first axis.

In the aforementioned contouring operation, a relative speed of thecutting blade to the work material, that is, a cutting speed correspondsto the sum of a circumferential speed of the cutting blade moving inresponse to rotation of the tool and a speed of a circular motionperformed by the cutting blade moving in response to revolution of thetool. According to the aforementioned conventional contouring operation,however, the tool is revolved by giving the spindle having the toolmounted thereon a circular motion, so that the speed of revolution isfar lower than the speed of rotation. Therefore, the cutting speed issubstantially determined by the speed of rotation of the tool, that is,the number of rotation of the spindle.

In a conventional apparatus using a mechanism of the so-called X-Ycoordinate system, the tool is revolved by coordinating the feeds of thespindle in the bisectional directions in the X-Y plane. This restrictionof control makes it difficult to revolve the machine tool at a higherspeed. When the spindle is moved in the bisectional direction, moreover,a spindle head is vertically moved along a column, and simultaneouslywith this, the column is horizontally moved on a bed. Thus, the membersto be moved have so large mass that the spindle cannot be revolved at ahigher speed.

On the other hand, the same problem may occur in an apparatus employingpolar coordinate system, in which a reciprocating motion of the main armis transmitted via its leading end to the tool shaft arm to cause thetool shaft to revolve. Specifically, the main arm is reciprocated with amotor imparting a reciprocating motion to the tool shaft arm and a motorrotating the tool shaft, and the tool shaft is revolved by driving thesetwo motors cooperatively, as in the aforementioned apparatus employingthe X-Y coordinate system. Therefore, it is difficult to increase thespeed of revolution of the tool shaft.

In still another type of apparatus, too, the tool shaft is revolved witha motor for rotating the tool shaft, so that the overall mass to berevolved is increased, which makes it difficult to revolve the toolshaft at a higher speed. In an apparatus constructed to revolve the toolshaft, the motor for rotating the tool shaft changes its positionaccording to a change of revolution radius of the tool shaft, so that aposition of the center of the gravity of a rotating member as a wholechanges. As the speed of revolution of the tool shaft is raised,therefore, its vibration may be increased.

In the prior art, in short, it is impossible to increase the speed ofrevolution of the tool shaft or the cutting tool mounted thereon, and aratio of revolution speed of the spindle to the cutting speed is notmore than 2 to 3%, so that the feed rate per revolution of the tool islowered. To enhance the working efficiency, therefore, the workingoperation has to be performed by increasing the speed of rotation of thetool or increasing the width of the cutting blade.

If the cutting width is increased, however, the area where chips contactwith the cutting blade is broadened, so that friction and heat isremarkably generated, thereby shortening the tool life. This results inthe disadvantage that the working efficiency is greatly restricted. Theaforementioned contouring work is the so-called intermittent cuttingoperation, in which the cutting blade bites into the work materialrepeatedly. In the method of the prior art as described above, on theother hand, the tool is revolved at a low speed and at a small feedrate, that is, the tool is rotated on its own axis at a high speed, thusincreasing the number of times that the cutting blade bites into thework material repeatedly. When this cutting operation is performed, inother words, many wide and long chips are produced. Therefore, an impactforce more frequently acts on the cutting blade. Moreover, this impactforce is strong, so that the possibility of shortening the tool life isincreased, which restricts the working efficiency.

The present invention has been made in consideration of the actual stateof art as described above, and has an object to provide an apparatus anda method capable of improving a working efficiency in a machiningoperation performed by rotating a tool and a workpiece relatively toeach other.

Another object of the invention is to provide an apparatus and a methodcapable of improving a working efficiency and a working accuracy bymaking it possible to vary a ratio between a number of rotation of thetool or the workpiece and a number of revolution of the tool or theworkpiece.

Still another object of the invention is to provide a machiningapparatus capable of raising a speed of revolution of the tool or theworkpiece at a high level.

Another object of the invention is to provide a machining apparatuscapable of changing a radius of revolution of the tool or the workpiecewhile rotating and revolving the tool or the workpiece.

Another object of the invention is to provide an apparatus and a methodcapable of improving the working efficiency without shortening the lifeof the tool.

DISCLOSURE OF THE INVENTION

The machining apparatus of the invention is provided with a spindlerotating while mounting a tool or a workpiece and a revolution shaftrotating on its center axis, and the spindle is rotatably held by therevolution shaft at a position offset from the center axis of therevolution shaft. This machining apparatus is also provided with arotation driving mechanism for transmitting a power through a rotatingmember rotating on a center axis of rotation of the revolution shaft ora member rotating integrally with the revolution shaft to the spindle torotate the same, while rotating the revolution shaft and the spindle atdifferent speeds respectively.

According to the machining apparatus of the invention, therefore, whenthe spindle and the revolution shaft are rotated on their respectivecenter axes, the tool or the workpiece mounted on a leading end of thespindle is rotated and revolved. By independently rotating therevolution shaft, in this case, the tool or the workpiece mounted on thespindle is revolved. Thus, the speed of revolution is not restricted, sothat it is possible to increase a ratio of speed by revolution in theworking speed, that is, a relative feeding speed or a feed rate betweenthe tool and the workpiece.

According to the machining apparatus of the invention, moreover, thereis provided a motor for revolution having a base portion on which therotation driving mechanism is fixed, a transmission mechanism forrevolution which transmits motive power from the motor for revolution tothe revolution shaft, a motor for the spindle fixed on the base portionand a transmission mechanism for the spindle which transmits motivepower from the motor for the spindle to the spindle.

With this construction, either of these two motors are fixed, and hencethe total mass of rotating elements is decreased, thereby raising thespeed of revolution of the spindle at a high level. The transmissionmechanism for the spindle is constructed such that torque is transmittedby a roller, thereby preventing fluctuation in rotation of the spindleto allow working operations having a high accuracy.

According to the machining apparatus of the invention, in the revolutionshaft, there is arranged an eccentric shaft rotating on an axiseccentric to the center axis of the revolution shaft. At the positioneccentric to the center axis of the eccentric shaft, there is rotatablyheld the spindle.

With this construction, the eccentricity of the tool or the workpiece tothe revolution shaft, that is, the revolution radius of the tool or theworkpiece is changed by rotating the eccentric shaft. This makes itpossible to voluntarily change a relative feed rate of the tool and theworkpiece or working radius. By rotating the eccentric shaft during theworking operation, moreover, working operations such as taper boring orrecessing operation can be performed.

The apparatus of the invention may be provided with a revolution radiuschanging mechanism for rotating the eccentric shaft relatively to therevolution shaft while permitting the eccentric shaft to rotateintegrally with the revolution shaft.

The additional provision of this revolution radius changing mechanismallows for the tool or the workpiece fixed to the spindle to rotate andrevolve while changing its revolution radius, which makes it easy toperform a working operation in which the radius of an object to beworked is changed, for example, a taper boring or recessing operation.

This revolution radius changing mechanism is also constructed to have adifferential mechanism for performing differential rotation by means ofthree rotating elements rotating relatively to one another. Among thesethree rotating elements, a first rotating element is connected to thetransmission mechanism for revolution, a second rotating element isconnected to the eccentric shaft and a third rotating element isconnected to a motor for changing revolution radius fixed to the baseportion.

Due to this construction, a mechanism for rotating the spindle, amechanism for revolving the spindle and a mechanism for changing radiusof revolution can operate independently form one another, and a heavymember such as a motor is not carried in a circular motion. This makesit possible to revolve the spindle at a higher speed and to freely set aratio of rotation number of the spindle to the revolution number of thesame accordingly and further to voluntarily change the revolution radiusof the spindle during its revolution.

In a machining apparatus provided with the aforementioned eccentricshaft, the spindle is balanced so that the center of gravity is alignedwith its center axis, the eccentric shaft having the spindle at itseccentric position is balanced so that the center of gravity is alignedwith its center axis, and the revolution shaft having the eccentricshaft fitted thereon holding the spindle rotatably is balanced so thatthe center of gravity is aligned with its center axis.

With this construction, even when the revolution radius of the spindleis changed by rotating the eccentric shaft, the position of the centerof gravity of the entire working apparatus does not changesubstantially.

As a result, even when the revolution number of the spindle isincreased, no vibration occurs. This makes it possible to increase therevolution speed of the spindle, that is, the tool or the workpiecewithout causing degradation in the working accuracy and increasing theload on the tool.

In the machining method of the invention, the tool and the workpiece arerotated relatively to each other, the amount of working of the tool perunit time is determined on the basis of at least one of a predeterminedmaximum sectional area to be worked and cutting speed. On the basis ofthe amount of working per unit time, there is determined a ratio of therotation number of the tool or the workpiece to the revolution numberthereof.

The tool or the workpiece is rotated and revolved so as to satisfy thisratio, thereby working the workpiece.

According to the method of the invention, therefore, it is possible toset a rotation number and revolution number which have excellent workingefficiency without shortening the life of the tool and increasing loadon the tool, and thus the efficiency of the working operation can beimproved.

In the method of the invention, moreover, the tool and the workpiece arebrought into contact with each other while being rotated and revolved.The ratio of rotation number of the tool to the revolution number of thesame is set to a value below 37, and the workpiece is intermittently cutby the cutting blade mounted on the tool.

According to the method of the invention, a relative feed between thetool and the workpiece is increased in the intermittent cuttingoperation in which the tool is rotated. For this reason, cutting amountor working efficiency is not decreased even if the cutting width perblade is reduced. In other words, as the cutting width per blade isreduced without degradation of working efficiency, heat generation,cutting resistance and impact force can be reduced, thereby improvingthe life of the tool. By increasing the cutting amount per blade withinthe tool life, moreover, the working efficiency can be improved.

In another method of the invention, the workpiece is cut by means of theblade while one of the tool having the blade and the workpiece isrotated and revolved. Of the cutting speeds at which the workpiece iscut by the blade, the ratio of cutting speed established by therevolution of the tool or the workpiece is set to not less than 7% tocut the workpiece intermittently.

According to the method of the invention, the relative feed between thetool and the workpiece can be increased, so that the load applied to thetool can be decreased according to the reduction of the cutting widthper blade to improve the tool life and to improve the working efficiencyby increasing the cutting amount within the life of the tool.

In the still another machining method of the invention, the machiningoperation is performed by rotating and revolving the tool or theworkpiece. The ratio of the rotation number to the revolution number ischanged on the basis of surface roughness of worked surface formed onthe workpiece to perform the aforementioned working operation.

According to the machining method of the invention, various workingoperations such as rough work or finish work can be performed by meansof one apparatus or tool, resulting in the reduction in not only cost ofinstallation but also in number of working steps to raise the workingefficiency to a higher level.

In still another method of the invention employing the aforementionedmachining apparatus, the machining operation is performed by moving thetool or the workpiece backwards and forwards relatively in the axialdirection while rotating and revolving the tool or workpiece.Simultaneously, the ratio of rotation number to revolution number israised between a working step for moving the tool or the workpieceforwards in the axial direction and working step for moving the tool orthe workpiece backwards in the axial direction.

According to this machining method, therefore, the rough work whereinthe ratio of rotation number to revolution number is decreased and thefinish work wherein this ratio is increased can be performed while thetool or the workpiece moves backwards and forwards in the axialdirection. As a result, a total working time can be shortened to improvethe productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing one embodiment of a machiningapparatus according to the invention.

FIG. 2 is a diagram for explaining the relative positions, as taken inthe radial directions, of a spindle, an eccentric shaft, a revolutionshaft and a retaining shaft of the apparatus.

FIG. 3 is a mechanical diagram for explaining a fundamental mechanismemployed in a differential mechanism.

FIG. 4 is an exploded schematic view of the components of thedifferential mechanism.

FIG. 5 is a diagram for explaining balance adjustment of individualshafts.

FIG. 6 is a flow chart for explaining a method for determining arotation/revolution ratio.

FIG. 7 is a schematic view showing loci of movement of a blade edge on aportion to be cut.

FIG. 8 is a diagram showing tendencies of changes in working efficiencyand working accuracy corresponding to changes in a rotation/revolutionratio, a tool diameter and the number of blades.

FIG. 9 is a schematic view showing a relative position between a tool inthe state where an inner face of a bore is cut by means of the machiningapparatus shown in FIG. 1 and a bore to be cut.

FIG. 10 is a diagram showing a result of determination of relationbetween the rotation/revolution ratio and the working accuracy.

FIG. 11 is a diagram showing a locus of the blade edge on the basis of amachining method of the invention.

FIG. 12 is a diagram showing a result of determination of relationbetween the rotation/revolution ratio and the working accuracy.

FIG. 13 is a front elevation schematically showing another embodiment inwhich the invention is applied to a lathe.

FIG. 14 is a plan view schematically showing another embodiment in whichthe invention is applied to the lathe.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will be specifically described with reference to theaccompanying drawings. First of all, a machining apparatus according tothe invention is described by adopting a cutting apparatus as anexample. In FIG. 1, a tool 1 is exemplified by a milling cutter havingcutting blades 3 formed on the outer circumference of a leading endportion of a shank 2, and a spindle 4 having the tool 1 mounted in itsleading end portion is arranged in a holding shaft 5. This holding shaft5 is formed into a cylindrical shape and integrated with an entirehousing (i.e., base portion) 7 of a cutting apparatus, as indicated byreference numeral 6 in FIG. 1. Therefore, the holding shaft 5 is movedwith respect to a (not-shown) workpiece to be cut, but will not rotateon its axis.

In this holding shaft 5, a revolution shaft 8 is rotatably held bybearings 9. In this revolution shaft 8, there is formed a bore, which isextended in the axial direction of and with an eccentricity to the axisof the revolution shaft 8 and in which an eccentric shaft 10 isrotatably held by bearings 11. Therefore, this eccentric shaft 10revolves around the axis of the revolution shaft 8 as this shaft 8rotates on its axis. This eccentric shaft 10 is provided for changingradius of revolution of the spindle 4. In this eccentric shaft 10, thereis formed a through bore, which is extended therethrough in the axialdirection of and with an eccentricity to the axis of the eccentric shaft10 and in which the spindle 4 is rotatably held by bearings 12.

FIG. 2 shows the relative positions of the aforementioned individualshafts in the radial directions schematically. As shown, the revolutionshaft 8 is arranged on the same axis as that of the holding shaft 5. Inthe revolution shaft 8, there is arranged the eccentric shaft 10 whichhas an axis O₁₀ at a position eccentric to the axis O₈ of the revolutionshaft 8. The spindle 4, as rotatably arranged in the eccentric shaft 10,is positioned eccentrically to the axis O₁₀ of the eccentric shaft 10.

As the eccentric shaft 10 is rotated, therefore, the spindle 4, aslocated outside of the axis O₁₀ of the eccentric shaft 10, moves on acircumference C₁₀ which is centered on the axis O₁₀. When theeccentricity of the eccentric shaft 10 to the revolution shaft 8 and theeccentricity of the spindle 4 to the eccentric shaft 10 are equal, theaxis O₄ of the spindle 4 may be aligned to the axis O₈ of the revolutionshaft 8 to reduce the eccentricity of the spindle 4 to the revolutionshaft 8 to zero. By rotating the eccentric shaft 10, more specifically,there is changed the eccentricity of the spindle 4, as arranged in theeccentric shaft 10, to the revolution shaft 8. When the eccentricity ofthe eccentric shaft 10 to the revolution shaft 8 and the eccentricity ofthe spindle 4 to the eccentric shaft 10 are equal, the eccentricity ofthe spindle 4 to the revolution shaft 8 is changed to zero or morewithin a limit of two times of the equal eccentricity.

The tool 1, as mounted in the spindle 4, rotates together with thespindle 4. Since this spindle 4 is held in the revolution shaft 8, onthe other hand, the spindle 4, i.e., a tool 1 revolves around the axisO₈ of the revolution shaft 8 as the revolution shaft 8 rotates on itsaxis. In this case, The radius of revolution of the spindle 4 determinesthe eccentricity of the spindle 4 to the revolution shaft 8, which isset by rotating the eccentric shaft 10.

This revolution shaft 8 is extended at its righthand end portion, asseen in FIG. 1, to the rear end portion of the housing 7 and isrotatably supported by the housing 7 through bearings 13 fitted on theouter circumference of its rear end portion. In the rear end portion ofthe revolution shaft 8, there is formed a concentric through hole, inwhich an input shaft 14 is rotatably held through bearings 15. Thisinput shaft 14 is provided for rotating the spindle 4 and is connectedto a spindle motor M1. This spindle motor M1 is fixed on the housing 7acting as the base portion. On the other hand, the input shaft 14 hasits lefthand end portion extended in the revolution shaft 8 to aposition close to the rear end portion of the spindle 4.

Moreover, a plurality of rollers 16 having different external diametersare arranged, being in contact with the outer surface of the input shaft14, at the end portion of the input shaft 14. These rollers 16 arerotatably mounted on support pins 17 which are mounted on the revolutionshaft 8 so as to be in parallel with the axis of the input shaft 14.Moreover, a cylindrical member 18 is fitted to enclose those rollers 16.Here, these rollers 16 are press-fitted between the cylindrical member18 and the input shaft 14 to transmit the torque through a frictionalforce because their contact pressures are high.

The cylindrical member 18 encloses the outer circumference of the rearend portion of the spindle 4. Between this outer circumference of thespindle 4 and the inner circumference of the cylindrical member 18,there are press-fitted a plurality of rollers 19 having differentexternal diameters like the aforementioned rollers 16. The rollers 19are rotatably supported by support pins 20, which are connected to aring-shaped gear 21 arranged rotatably around the outer circumference ofthe spindle 4 through a bearing. The ring-shaped gear 21 is furtherconnected to the rear end portion of the aforementioned eccentric shaft10 by pins.

Thus, the torque of the input shaft 14 is transmitted to the cylindricalmember 18 by the rotations of the rollers 16 contacting with the outercircumference of the input shaft 14, and the torque of the cylindricalmember 18 is transmitted to the spindle 4 by the rotations of therollers 19 contacting with the inner circumference of the cylindricalmember 18. In short, as the input shaft 14 is rotated by the motor M1,its torque is transmitted to rotate the spindle 4. As the individualrollers 16 and 19 revolve relative to one another, moreover, there ischanged the eccentricity of the spindle 4 to the input shaft 14, namely,the revolution radius of the spindle 4.

In the portions of the revolution shaft 8 on the side of the outercircumference of the ring-shaped gear 21, there are formed a pluralityof cut-away portions which are opened in the inner and outercircumferences and in which there are arranged intermediate gears 22meshing with the ring-shaped gear 21. The thicknesses of therevolutionary shaft 8 at the individual portions, in which theintermediate gears 22 are arranged, are made different from one anotherbecause the axes of the bores extending in the axial direction areeccentric to the axis of the revolution shaft 8. Therefore, the externaldiameters of the individual intermediate gears 22 are made differentaccording to the thicknesses of the revolution shaft 8 at thoseindividual portions. In other words, the circle joining the outermostcircumferences of the individual intermediate gears 22 is centered onthe axis of the revolution shaft 8. Here, the individual intermediategears 22 are rotatably supported by support pins 23 which are mounted onthe revolution shaft 8.

On the other hand, the individual intermediate gears 22 mesh with arevolution radius changing gear 24 acting as an internal gear. Thisrevolution radius changing gear 24 is formed in the inner circumferenceof the leading end portion of a cylindrical shaft 25. This cylindricalshaft 25 is fitted coaxially with the input shaft 14 on the outercircumference of the revolution shaft 8 and is rotatably held bybearings 26.

On the outer circumference of the revolution shaft 8, as located on theouter circumference of the input shaft 14, there is fixed a revolutionshaft gear 27. Adjacent to this revolution shaft gear 27, there isarranged an intermediate shaft gear 28 which is fixed on theaforementioned cylindrical shaft 25. The revolution shaft gear 27 mesheswith an input gear 30 in a differential mechanism 29, and theintermediate shaft gear 28 meshes with an output gear 31 in thedifferential mechanism 29.

Here will be described this differential mechanism 29. The differentialmechanism 29 is constructed by making use of the mechanism having aconstruction shown in FIG. 3. In FIG. 3, more specifically, aring-shaped member 100 is splined in its inner circumference to haveteeth 101, and external teeth 102 having a smaller number of teeth thanthe teeth 101 are formed on a flexible ring 103 which is rotatablyarranged in the inner circumference of the ring-shaped member 100. Inthe inner circumference of the flexible ring 103, there is arrangedthrough a bearing 105 an elliptical rotary member 104, which has twolonger-diametrical end portions pushing the flexible ring 103 intomeshing engagement with the teeth 101 of the ring-shaped member 100. Inthe mechanism shown in FIG. 3, therefore, the number of teeth of theflexible ring 103 is less than that of the ring-shaped member 100. As aresult, even when the flexible ring 103 makes one rotation, thering-shaped member 100 does not make one rotation to have the angle ofrotation which is reduced by the difference in the number of teeth.

FIG. 4 shows the differential mechanism 29 schematically in an explodedview. This differential mechanism 29 includes: a pair of circularsplines 32 and 33 corresponding to the aforementioned ring-shaped member100; a flexible spline 34 corresponding to the aforementioned flexiblering 103 to mesh with those circular splines 32 and 33; and a wavegenerator 35 fitted in the inner circumference of the flexible spline 34and corresponding to the elliptical rotary member 104. Morespecifically, the differential mechanism 29 includes: the pairedcylindrical circular splines 32 and 33 having the splined innercircumferences; the flexible spline 34 made of a flexible cylindricalmember and splined in its outer circumference to mesh with the splinedteeth of the circular splines 32 and 33; and the wave generator 35equipped with an elliptical cam having an outer periphery fitting a ballbearing which fits the flexible spline 34 on its outer periphery.

One circular spline 32 is set to have a number of teeth (e.g., 200)equal to that of the flexible spline 34 and is fitted and fixed in theinner circumference of the input gear 30. On the other hand, the othercircular spline 33 is set to have a slightly larger number of teeth(e.g., 202) than the flexible spline 34 and is fitted and fixed in theinner circumference of the output gear 31. Moreover, the wave generator35 is fixed on an adjusting shaft 36, which is connected to a radiuschanging motor M2. Here, this radius changing motor M2 is fixed on thehousing 7 corresponding to the base portion.

In this differential mechanism 29, therefore, when the input gear 30 isrotated with the wave generator 35 or the adjusting shaft 36 beingfixed, the flexible spline 34 rotates at the same rotation number asthat of the input gear 30, because the number of teeth of the circularspline 32 fixed in the input gear 30 is equal to that of the flexiblespline 34. On the contrary, the number of teeth of the circular spline33 fixed in the output gear 31 is larger than that of the flexiblespline 34, so that the output gear 31 is decelerated to rotate accordingto the difference in the number of teeth. In the embodiment thus fardescribed, the flexible spline 34 has the number of teeth “200” whereasthe circular spline 33 has the number of teeth “202”, so that the outputgear 31 is decelerated to rotate at a ratio of 200/202=100/101.

Thus, there arises a difference in the number of rotations, but, even insuch a case, a ratio of number of teeth between the input gear 30 andthe revolution shaft gear 27 and a ratio of number of teeth between theoutput gear 31 and the intermediate shaft gear 28 are so set that therevolution radius of the spindle 4 may not change. When the input gear30 has the number of teeth “100” whereas the revolution shaft gear 27has the number of teeth “200”, for example, the output gear 31 is set tohave the number of teeth “101” whereas the intermediate shaft gear 27 isset to have the number of teeth “200”. In the case of this construction,the input gear 30 is rotated at 101 rpm, for example, with the adjustingshaft 36 or the wave generator 35 being fixed. Then, the output gear 31rotates at 100 rpm whereas the revolution shaft gear 27 rotates at 101/2rpm. Moreover, the output gear 31 rotates at 100 rpm so that the meshingintermediate shaft gear 28 rotates at 100×101/200=101/2 rpm. In short,the revolution shaft gear 27 and the intermediate shaft gear 28 rotateat an equal speed.

Therefore, the number of rotations of the revolution shaft 8 and thenumber of rotations of the cylindrical shaft 25 become equal. As aresult, there rotate altogether the revolution radius changing gear 24formed on the cylindrical shaft 25, the intermediate gears 22 meshingwith the first gear 24, and the ring-shaped gear 21 meshing with thesecond gears 22. In short, the phases of the individual rollers 16 and19 are kept constant in the direction of revolution.

Because of the difference in the number of teeth between the flexiblespline 34 and the circular spline 33 on the side of the output gear 31,on the other hand, the circular spline 33 is decelerated at a ratecorresponding to the difference in the number of teeth with respect tothe rotation of the flexible spline 34. In the aforementionedembodiment, the difference in the number of teeth is “2”, so that thecircular spline 33 is decelerated at a rate of 2/200=1/100 with respectto the rotation of the flexible spline 34. In other words, when theflexible spline 34 is rotated at 100 rpm together with the adjustingshaft 36, the circular spline 33 relatively rotates at minus (−) 1 rpm.Here, no difference occurs in the number of rotations between thecircular spline 32 on the side of the input gear 30 and the flexiblespline 34, because they have an equal number of teeth. After all, whenthe flexible spline 34 is rotated together with the adjusting shaft 36,a difference occurs between the rotational phases of the input gear 30and the output gear 31. In other words, it is possible to establish therelatively rotational motions between the input gear 30 and the outputgear 31 at the rotational speed of 1/100 of the number of rotations ofthe adjusting shaft 36.

This relative rotation appears as a relative rotation between therevolution shaft 8 and the ring-shaped gear 21, namely, as a relativespeed of revolutions between the individual rollers 16 and 19. Moreover,these relative revolutions between the individual rollers 16 and 19change the eccentricity of the spindle 4 to the input shaft 14, i.e.,the revolution radius, so that the apparatus thus far described can makeit easy to adjust the revolution radius finely. Here, reference numeral37 in FIG. 1 indicates a revolution gear, which meshes with theaforementioned input gear 30. To this revolution gear 37, moreover,there is connected a revolution motor M3, which is fixed on the housing7. On the other hand, the aforementioned revolution radius changingmotor M2, the differential mechanism 29, the line for transmitting thetorque from the differential mechanism 29 to the revolution shaft 8, andthe line for transmitting the torque from the differential mechanism 29to the eccentric shaft 10 construct a revolution radius changingmechanism altogether.

In the cutting apparatus shown in FIG. 1, moreover, the revolutions ofthe spindle 4 are achieved not by the combination of the linear motionsin the two-dimensional directions but by the rotations of the revolutionshaft 8 enclosing the spindle 4 so that the spindle 4 can be rotated andrevolved at high speeds. In the aforementioned example, on the otherhand, the eccentricity of the spindle 4 to the revolution shaft 8 can bechanged by the rotation of the eccentric shaft 10, so that therevolution radius of the spindle 4 can be changed. It is, therefore,possible to easily perform the cutting operations of tapered holes, theboring operations for a plurality of kinds of different internaldiameters, and the recessing operations.

Here, the line for transmitting the torque from the motor M1 for thespindle 4 corresponds to a transmission mechanism for rotating thespindle of the invention, the line for transmitting the torque from themotor M3 for revolution to the revolution shaft 8 corresponds to atransmission mechanism for revolution of the invention and a mechanismhaving combination of these two transmission mechanism corresponds to arotation driving mechanism of the invention.

When the cutting operation is performed by mounting the tool 1 on thespindle 4, the spindle 4 and the revolution shaft 8 are turned to rotateand revolve the spindle 4, and the eccentric shaft 10 is rotated tochange the revolution radius of the spindle 4. The aforementioned threeshafts are balanced as described hereinafter so as to prevent vibrationwhich occurs when the individual shafts are rotated.

FIG. 5 is a diagram for explaining the balance adjustment of theindividual shafts. With the tool or a weight equal to the same beingmounted on the leading end of the spindle 4, the spindle 4 is balancedso that the center of gravity is aligned with a center axis O₄. Thisbalance adjustment can be made by adding/removing a predetermined massWb, for example, by cutting away a portion from the outer circumferenceof the spindle 4 or mounting a weight for adjustment such as a screw.The balance adjustment is made not only in the radial direction but alsoin the axial direction.

The eccentric shaft 10 is balanced so that the center of gravity as awhole is aligned with a center axis O₁₀, with the spindle 4 thusbalanced being assembled at a position offset from this center axis O₁₀.This balance adjustment can be made by applying/removing thepredetermined weight Wb on or from a portion of the outer circumferenceof the eccentric shaft 10 as in the aforementioned example.

The revolution shaft 8 is balanced so that the center of gravity isaligned with its center axis O₈ by applying/removing the predeterminedweight Wb on or from a portion of its outer circumference, with theeccentric shaft 10 on which the spindle 4 is attached and balanced asdescribed before being located at a position offset from the center axisO₈. The revolution shaft 8 and the eccentric shaft 10 are also balancedin their axial directions.

When the revolution shaft 8 is rotated to revolve the spindle 4, thecenter of gravity as a whole is aligned with the center axis O₈ of therevolution shaft 8, and therefore no vibration occurs even if thespindle 4 is revolved at a high speed, whereby at least the off-set loadand resultant vibration are prevented or suppressed. Such a state ismaintained even when the revolution radius of the spindle 4 is changed.In short, each of the spindle 4 and the eccentric shaft 10 is balancedso that the center of rotation is aligned with the center of gravity.The spindle 4 and eccentric shaft 10 thus balanced are held by therevolution shaft 8, so that the center of gravity substantially isaligned with the center axis O₈. For this reason, even when the positionof the spindle 4 in the radial direction is changed by rotation of theeccentric shaft 10, the position of the center of gravity as a wholedoes not change. Both before and after revolution radius of the spindle4 is changed, therefore, there occurs no change in the balance, so thatvibration can be effectively prevented or suppressed even if the spindle4 is rotated at a high speed.

Here will be described a method of machining the workpiece by means ofthe machining apparatus of the invention. In the cutting apparatusaccording to the invention, as described hereinbefore, the spindle motorM1 and the revolution motor M3 individually fixed on the housing 7 areactivated to rotate and revolve the spindle 4, that is, the tool 1attached thereto. This makes it possible to raise the speed ofrevolution to a higher level than the conventional methods and toappropriately set the ratio K between the rotation number of the tooland the revolution number of the same accordingly. This ratio Kseriously affects the tool life and the working efficiency and istherefore determined first of all.

FIG. 6 is a flow chart showing a method of determining arotation/revolution ratio K, an initial value of which is first set (atStep S1). If this rotation/revolution ratio K is “7”, the tool 1 makesone revolution while rotating on its own axis once. This can be appliedto the boring operation. The contouring operation for intermittentlycutting workpiece is performed when the rotation/revolution ratio K is avalue exceeding “1”. Thus, a smaller value of those ensuring thecontouring work, for example, an integer “2” is adopted as an initialvalue of the rotation/revolution ratio K.

On the other hand, a tool to be employed is decided on the basis ofmaterial or shape of workpiece to be cut, so that the number of blades Zof the tool is indicated (at Step S2) and a tool diameter D1 is also set(at Step S3).

A thickness t to be cut is calculated on the basis of theserotation/revolution ratio K, the number of blades Z of the tool and adiameter D0 of a bore to be worked of the product (at Step S4). FIG. 7is a schematic enlarged diagram of a cut portion, a line indicated bythe reference numeral C1 is a locus of a leading blade and a lineindicated by the reference numeral C2 is a locus of a subsequent blade.These loci of the individual blades are formed by rotating and revolvingthe tool. At Step S4, there is calculated a width of a portion where aninterval between the loci of the individual blades is largest. Thiscalculation can be geometrically made on the basis of the respectivedata concerning the tool such as Z, D1 and the rotation/revolution ratioK.

On the other hand, a maximum cutting sectional area A is indicated (atStep S5). This maximum cutting sectional area A is an instantaneousmaximum value during the cutting operation and is set on the basis ofcurrent data such as data in the boring operation for a tool.Specifically, load applied to each blade of the tool is raised accordingto a cutting sectional area, and the maximum cutting sectional area tobe allowed for the tool is preset as data for the tool. At Step S5, themaximum cutting sectional area A is set on the basis of the theseexisting data.

A cutting width fz (=A/t) is calculated on the basis of the cutthickness t calculated at Step S4 and the maximum cutting sectional areaA set at Step S5 (at Step S6).

Moreover, a cutting speed V is set as a condition of a tool to beemployed (at Step S7). The cutting speed V is a relative speed of thecutting blade to the workpiece. The cutting blade is liable to berapidly worn away, the higher the cutting speed V becomes, so that thetool life is shortened. From the cutting conditions, therefore, there isdetermined the tool life, and the cutting speed V is set on the basis ofthis tool life.

The cutting speed V is a sum of the circumferential speed of the cuttingedge caused by rotation of the tool and the circumferential speed of thecutting edge moved by revolution of the tool. Thus, the revolutionnumber N is calculated on the basis of the rotation/revolution ratio Kset at Step S1 and the cutting speed V set at Step S7 (at Step S8).Specifically, the revolution number N is determined by the followingformula, wherein D0 is a diameter of a bore to be cut and D1 is adiameter of the tool.

N=V×1000/[π×{D0+D1(K−1)}]

Here, the cutting speed V is expressed by the sum of a cutting speed VAof the revolving tool and a cutting speed VB of the rotating tool, andthe individual cutting speeds VA and VB are determined by the followingFormulas.

VA=N×D 0×π

VB=N×(K−1)×D 1×π

Thus, the working efficiency Q is calculated (at Step S9). This workingefficiency Q is a cutting amount per unit time and calculated on thebasis of the revolution number N, the cutting width fz, the workingdiameter D0 and a raw material diameter D2. It is decided (at Step S10)whether the working efficiency Q thus calculated satisfies requirement.This decision is made on the basis of a demanded cycle time of thecutting operation, for example.

If the answer of Step S10 is negative, it is decided (at Step S11)whether the cutting speed V can be increased. When a cutting speed isset to a smaller value than the maximum cutting speed allowed for thetool at Step S7, the answer of Step S11 is affirmative, and the routineadvances to Step S7, at which the cutting speed V is increased within anallowable range. In short, the cutting condition is changed to increasethe working efficiency Q.

If the answer of Step S11 is negative, on the contrary, it is decided(at Step S12) whether the cutting sectional area A can be increased. Ifthe maximum cutting area A is set to a smaller value than the maximumvalue at Step S5, the answer of Step S12 is affirmative, then theroutine advances to Step S5, and the maximum cutting sectional area Ahas a large value. In short, the cutting condition is changed toincrease the working efficiency Q.

If the answer of Step S12 is negative, on the contrary, it is decided(at Step S13) whether the tool can be changed for one having a largenumber of blades Z. In short, this possibility of change is decided dueto whether or not there is a prepared tool. If the change with a toolhaving a large number of blades Z is possible, the routine advances toStep S2, and a newly selected number of blades Z is indicated. In thiscase, the number of blades Z is increased, so that the cuttingconditions are changed to increase the working efficiency Q.

If the answer of Step S13 is negative because the change of the tool isnot possible, the rotation/revolution ratio K is lowered, in short, thenumber of revolution is relatively increased, so that the unit cuttinglength per blade is increased and the working efficiency is increased.

Here, in the aforementioned steps, the cutting conditions are selectedon the basis of the result of decision of the working efficiency Q, butthe rotation/revolution ratio K is set to a small value in Step S1, sothat a high working efficiency is gained. Therefore, there is generallyno possibility that the answer of Step S10 is affirmative and the changeof the working condition indicated at the beginning is required.

After the decision on the working efficiency Q is made as describedbefore, the working accuracy is decided. Because the cutting blade makesa rotationary motion as shown in FIG. 7, the inner face of the workpieceis cut away to form an arc-shaped recess. While a portion remained aftercut by the blade is cut in by the following blade, the tool slightlymoves in the circumferential direction of the worked bore according tothe revolution speed. Therefore, there remains a ridge having atriangular section whose height is indicated by the reference numeral Hin FIG. 7. The height H of the ridge is related to the moving distanceof the tool till the following blade cuts in the workpiece, that is, therevolution speed of the tool, as shown in FIG. 7, and the height Hbecomes larger as the revolution number increases. If the result ofdecision on the working efficiency Q is affirmative, therefore, theroutine advances to Step S15 and a geometrical height H of the ridge orthe remaining portion after cut is calculated using therotation/revolution ratio K (at Step S15).

This height H appears as the error in the cutting depth or surfaceroughness and is therefore decided in contrast with a demanded accuracy(at Step S16). As the revolution speed or revolution number of the toolis increased, the moving distance of the tool during the rotationthrough a predetermined angle is increased, and the height H of theridge left after cut is increased accordingly. In case the initial valueof the rotation/revolution ratio K is set to a small value, therefore,the height H is increased and the working accuracy is lowered. In thecase of the rough machining, for example, the answer of Step S16 may beaffirmative, even if the rotation/revolution ratio K is an initialvalue. In this case, there is adopted a value of the rotation/revolutionratio K, the cutting conditions such as the rotation number, revolutionnumber or feeding speed of the tool are set. Here, the rotation numbercan be determined by multiplying the revolution number N determined atStep S8 by the rotation/revolution ratio K (N×K).

On the contrary, the more closely the locus of the blade approximates astraight line, that is, the larger the tool diameter D1 is, the height His smaller, so that the working accuracy is improved. In case the answerof Step S16 is negative because the height H of the protruding portionleft after cut is so large as not to meet requirement, therefore, it isdecided (at Step S18) whether the tool diameter D1 can be increased,that is, whether the tool can be changed for a tool having a largerdiameter D1.

If the answer of Step S18 is affirmative, the routine advances to StepS3 and a diameter D1 of a new tool is indicated. On the contrary, if theanswer of Step S18 is negative, it is decided (at Step S19) whether thecurrent tool can be changed for a tool having a large number of bladesZ. As described above, specifically, as the moving distance of the toolin the interval between the time when the leading blade cuts in theworkpiece and the time when the following blade cuts in the workpieceincreases, the height H of the protruding portion left after cut becomeslarger. Therefore, if the interval between the leading blade and thefollowing blade is short because of the number of blades being large,the height H of this protruding portion is reduced. In case the diameterD1 of the tool cannot be increased, therefore, it is decided whether thenumber of blades Z can be increased. If the answer of this step isaffirmative, the routine advances to Step S2 and the number of blades Zof a new tool is indicated.

On the contrary, If the answer of Step S19 is negative, therotation/revolution ratio K is increased (at Step 20). In short, themoving distance of the tool towards the circumferential direction of thebore to be worked is reduced by relatively lowering the revolutionnumber.

In case the diameter D1 of the tool is increased because an affirmativedecision is made at Step S18, or in case the number of blade Z isincreased because an affirmative decision is made at Step S19, or incase the rotation/revolution ratio K is raised at Step S20, the workingefficiency Q is changed according to the changes in these workingconditions. Therefore, the aforementioned routines from Step S4 to StepS10 are executed to make the calculation and decision of the workingefficiency Q again. In case the decision on the working efficiency Q isaffirmative or in case the working conditions are changed on the basisof the calculation and the decision of the working efficiency Q, theheight H of the protruding portion left after cut is calculated again(at Steps S15) and the decision on this height H is made (at Step S16).Thus, there is determined the rotation/revolution ratio K whichsatisfies the requirements of the working efficiency Q and the workingaccuracy, and the cutting conditions such as rotation number, revolutionnumber or feeding speed are set on the basis of this rotation/revolutionratio K.

FIG. 8 is a diagram showing the tendencies for the working efficiency Qand the working accuracy (the aforementioned height H) to changeaccording to the rotation/revolution ratio K, the diameter D1 of thetool and the number of blades Z. In short, the larger therotation/revolution ratio K becomes, the higher the working efficiency Qbecomes and the lower the working accuracy becomes. On the other hand,the larger the diameter D1 of the tool becomes, the higher the workingaccuracy becomes. As the number of blades Z is increased, the workingaccuracy becomes higher.

On the basis of the cutting conditions thus set, there are controlledthe speeds of the spindle motor M1 and the motor M3 for revolution.Moreover, the cutting operation is performed by moving the spindle 4together with the holding shaft 5 in the axial direction. FIG. 9 is aschematic diagram showing the state where a boring operation isperformed using the tool 1 mounted on the cutting apparatus describedhereinbefore. By activating the spindle motor M1, the tool 1 is rotatedon its own axis O¹ (i.e. the axis O₄ of the spindle 4). Simultaneously(at the same time), by activating the motor M3 for revolution, therevolution shaft 8 is rotated, and the spindle 4 or the tool 1 isrevolved on the axis O₈ of the revolution shaft 8, that is, the centeraxis O₄₀ of the bore 40 to be worked.

While the spindle motor M1 and the motor M3 for revolution areactivated, therefore, the holding shaft 5 is moved and inserted into thebore 40 to be worked by the tool 1. The tool 1 is rotated and revolved,so that the workpiece 1 is cut by the cutting blade 3, mounted on theouter circumference of the leading end of the tool 1, at cutting speeddetermined by adding the circumferential speed of the tool 1 beingrotated to the speed at which the tool 1 being revolved is fed in thecircumferential direction of the bore 40 to be worked. In this case, theapparatus shown in FIG. 1 is almost free from restriction on therevolution speed of the tool 1, so that the cutting operation isperformed by increasing the revolution speed. Specifically, therotation/revolution ratio K is set to be smaller than “37”. Moreover, asthe revolution number is increased, the cutting width is reduced. Thisis done because the increase in the revolution number causes the feed ofthe tool to increase, resulting in the increase of the length of chipsand the cutting amount.

FIG. 10 is a diagram showing the result of measurement of relationsbetween the rotation/revolution ratio K and the working efficiency.Here, the working efficiency is expressed by cutting volume (cc) perunit time (min). This determination result is obtained in the case wherea bore having an internal diameter of 55 mm is cut at the cutting speedof 200 m/min and by the cutting width of 0.6 mm. The tools employed arean end mill having an outer diameter of 20 mm and an end mill having anouter diameter of 50 mm.

Since the revolution number is large, as shown in FIG. 10, the smallerthe rotation/revolution ratio K becomes, the more the working efficiencyincreases. When the rotation/revolution ratio K becomes smaller than“37”, the tendency for the working efficiency to increase becomesremarkable. Specifically, the working efficiency obtained in the casewhere the rotation/revolution ratio K is smaller than “20” is twice ormore the working efficiency obtained when the rotation/revolution ratioK is set to around “100”. In FIG. 10, incidentally, the workingefficiency in the case of the rotation/revolution ratio K being “1” isthat of the boring operation or continuous cutting operation. Thecutting speed in the contouring work is the sum of the speed at whichthe blade is rotated when the tool is rotated and the speed at which theblade is fed when the tool is revolved. However, the aforementionedcutting apparatus of the invention sets no limit to the revolutionnumber, resulting in the increase of the speed at which the blade is fedwhen the tool is revolved. Specifically, in this invention, the ratiobetween the speed at which the blade is fed by the revolution of thetool and the cutting speed is set to be more than 7%. This setting maybe made by changing either the revolution radius or the revolutionnumber.

In the contouring work in which the tool is rotated and revolved, thetool is fed by a predetermined distance while the blade makes one turn,so that the edge forms loop-shaped loci along the inner circumferentialface of the bore 40 to be worked. Therefore, there is produced a part ofthe workpiece over which the tool is fed while the edge is not appliedon the workpiece. In short, this part remains as a portion left aftercut, while projecting towards the center of the bore 40 to be worked.The height H of the portion left after cut can be employed as areference value for the working accuracy. FIG. 12 is a diagram showingthe result of measurement of relations between the rotation/revolutionratio K and the working accuracy H (μm). The cutting conditions underwhich this measurement has been made are: an inner diameter of the boreto be worked=55 mm; the cutting speed=200 m/min; and the cuttingwidth=0.6 mm. The tools employed are: an end mill having the outerdiameter of 20 mm and 8 blades; an end mill having the outer diameter of20 mm and 16 blades; an end mill having the outer diameter of 50 mm and8 blades; and an end mill having the diameter of 50 mm and 16 blades.

The cutting apparatus of this invention sets no limit to the revolutionnumber, so that the rotation/revolution ratio K can be reduced to “1”,in which the continuous cutting operation is made, and the workingaccuracy can be voluntarily set accordingly. In short, in the cuttingmethod of the invention, the rotation/revolution ratio K is set on thebasis of the working accuracy, that is, the roughness of surface to beworked. Thus, various cutting operations from rough machining to finishmachining can be performed without changing tools. In case the innerface of a predetermined bore is worked, for example, the rough machiningis performed at the feeding stroke by reducing the rotation/revolutionratio K and the finish machining having a high working accuracy isperformed at the return stroke by increasing the rotation/revolutionratio K. This makes it possible to finish the work of products in ashort period of time and improve the productivity.

Here will be enumerated the example of the machining method of theinvention and the example of the convention end milling.

Example of Contouring Work of the Invention

Here, a diameter of the bore to be worked is 65 mm, a diameter of thetool is 25 mm, and the number of blades is 8. The cutting speed is setto 200 m/min, in which the speed of the tool being rotated is 142.1m/min (71.05%) and the speed of the tool being revolving is 57.9 m/min(28.95%). In this case, the rotation/revolution ratio K is1809.3/283.5=6.38 (<37). Therefore, the feed rate per blade is 4 mm, andthe cutting width in axial direction is set to 1 mm and shared by 51blades. Moreover, the depth of cut in radial direction is set to 2 mm.The time required to the cutting operation is 1.1763 mins. The number ofworkpieces machined until the wear rate of the flank becomes 0.3 mm is200.

Example of Conventional End Milling

Here, a diameter of the bore to be worked is 65 mm, a depth of work is50 mm, a diameter of the tool is 25 mm, the number of blades is 8. Thecutting speed is set to 200 m/min, in which the speed of the tool beingrotated is 196.99 m/min (98.5%) and the speed of the tool beingrevolving is 3.01 m/min (1.5%). In this case, the rotation/revolutionratio K is 196.99/3.01=65.45 (>37). Therefore, the feed rate per bladeis 0.15 mm, and the cutting width in axial direction is set to 4 mm(cutting width per blade). Moreover, the depth of cut in radialdirection is set to 2 mm. The time required to the cutting operation is0.8481 mins. The number of workpieces machined until the wear rate ofthe flank becomes 0.3 mm is 20.

According to the method of the invention, as clarified by these examplesof the cutting operations, even if the cutting width of the bore to beworked in the axial direction is small, the cutting operation isfinished in a short period of time and the working efficiency can beraised more than ever before. Moreover, the life of tool can be improvedover that of the prior arts. These improvements may be made on the basisof the fact that the feeding rate per blade is large, so that thefrequency of impact acting on the edge or impact force is reduced andalso the fact that the cutting operation of the invention is anintermittent one differently from the boring operation, so that the edgecan be air-cooled, whereby wear caused by adhesion or oxidization can besuppressed and damage such as chipping caused by mechanical shock can bealso suppressed.

The invention has been hereinbefore described on the basis of thespecific embodiment. However, the invention should not be limited to theforgoing specific embodiment, but the eccentric shaft 10 shown in FIG. 1may be replaced by a fixed shaft which is incapable of rotating, forexample. Even if the apparatus of the invention has such a construction,the cutting operation in which the feeding rate is large can beperformed by increasing the revolution number. In the construction shownin FIG. 1, moreover, the torque is transmitted through a roller or agear. The transmission of the torque may be always transmitted through agear or a roller, or may be transmitted through a winding transmissiondevice using a chain and the like. The cutting apparatus of theaforementioned specific embodiment is constructed to use a motor forrotation, a motor for revolution and a motor for changing revolutionradius. But, either of these three motors may be removed and replacedwith a speed changing mechanism, through which torque may be distributedbetween the motor for rotation, the motor for revolution and the motorfor changing revolution radius. The differential mechanism of theinvention is not limited to the construction described in the forgoingspecific embodiment but may be constructed to make differential actionsby rotating the three rotary elements relatively to each other.

In the foregoing specific embodiment, there is adopted the case wherethe inner face of the bore is cut as an example. According to the methodof the invention, however, various cutting operations can be performed;for example, cutting of the outer surface of a shaft, cutting of theinner face of a tapered bore or cutting of the outer face of a taperedshaft. In the taper cutting of this kind, the revolution radius of thetool is changed by continuously rotating the eccentric shaft 10 shown inFIG. 1 during the cutting operation, whereby allowing the taper cuttingto be easily performed. Moreover, the method of the invention can beapplied to the cutting of the external and internal threads or drillingoperations. In any one of these cutting operations, the workingefficiency can be improved by increasing the number of revolution andraising the feed rate more than that of the prior arts.

Moreover, the method of the invention can be applied to a machiningapparatus which rotates the workpiece instead of the tool. Such anapparatus is exemplified by a lathe shown in FIGS. 13 and 14. This latheis provided with a base 200, an X axis table 201 and a Y axis table 202.On the bed 200, there is arranged the X axis table 201 and the Y axistable 202 stacked in an upper and lower two stages. In short, the X axistable 201 is arranged on the bed 200 through a linear guiding mechanism203 moving in the direction perpendicular to the longitudinal directionof the bed 200. The Y axis table 202 is arranged on the X axis table 201through a linear guiding mechanism 204 moving in the longitudinaldirection of the bed 200. On the Y axis table 201, there is fixed theapparatus shown in FIG. 1, in which the axis of the spindle 4 isparallel to the moving direction of the Y axis table 202. In theapparatus shown in FIGS. 13 and 14, at the leading end of the spindle 4,there is fitted a chuck 206 holding a workpiece 205.

At one end portion of the bed 200 in the longitudinal direction,moreover, there is fitted a column 207 extending in the verticaldirection. On the upper end portion of the column 207, there is mounteda tool head 208, to which a tool 209 such as a bit is fitted andprojected toward the chuck 206. On the both sides of the column 200 inthe moving direction of the X axis table 201, there are located aloading portion 210 and an unloading portion 211 for the workpiece 205.By moving the X axis table 201, therefore, the chuck 206 fitted to thespindle 4 is moved to respective positions facing the loading portion210, the tool 209 and the unloading portion 211. By moving the Y axistable 202, moreover, the chuck 206 is moved backwards and forwards withrespect to each of the loading portion 210, the tool 209 and theunloading portion 211.

According to the machining apparatus having a construction shown inFIGS. 13 and 14, the workpiece 205 held by the chuck 206 is moved towardthe tool 209 while the spindle 4 is rotated and revolved. Therefore, theworkpiece 205 can be lathed by the tool 209. In this case, the workpiece205 comes into contact with the tool 209 while rotating and revolvingwith the spindle 4, so that the workpiece 205 and the tool 209 areintermittently brought into contact with each other, whereby theintermittent cutting operation is performed. Therefore, chips generatedduring the cutting operation are broken into short segments, therebybeing effectively exhausted in addition to the improvement in theworking efficiency and surface roughness obtained in the foregoingspecific embodiment.

Moreover, the invention is not limited to the apparatus and method forthe cutting operations as described hereinbefore but can be applied toan apparatus and a method for performing other machining operations suchas a grinding. In the invention, moreover, the cutting operation can beperformed by moving the tool and the workpiece relatively to each other.Therefore, as one of the tool and the workpiece is rotated and revolved,the other of the tool and the workpiece is moved in the direction of atleast one of three axes orthogonally crossing with each other to performthe cutting operation.

According to the invention, as described hereinbefore, the revolutionshaft holding the spindle at an offset position is rotated on its ownaxis while the spindle is rotated, whereby allowing the tool or theworkpiece mounted on the leading end of the spindle to be rotated andrevolved. In this case, the revolution speed is not specificallyrestricted, so that the ratio of the speed by revolution to the cuttingspeed, that is, the relative feeding speed and feeding amount betweenthe tool and the workpiece can be increased. According to the invention,therefore, the working efficiency can be improved, for example, byincreasing the feeding amount in the contouring work. At the same time,the cutting width can be reduced without lowering the workingefficiency, whereby the load on the edge is reduced and the life of thetool can be improved.

According to the invention, furthermore, both the motor for rotating thespindle and the motor for revolving the spindle can be fixed. With thisconstruction, it is possible to reduce the mass to be rotatedsimultaneously with the revolution of the spindle, so that therevolution speed of the spindle can be raised to a high level. Byemploying a roller on a mechanism transmitting torque for rotating thespindle or a mechanism transmitting torque for revolving the spindle,moreover, it is possible to make rotation and revolution in which lessoscillation or fluctuation is generated, and thereby the workingaccuracy can be improved.

The apparatus of the invention is provided with the aforementionedeccentric shaft, the rotation of which changes the off-set ratio of thetool or the workpiece to the revolution shaft. Therefore, the feedingamount or working radius of the tool or the workpiece can bevoluntarilly changed. By rotating the eccentric shaft during the cuttingoperation, morevoer, the taper cutting and the recessing operation canbe performed.

Due to this construction, a mechanism for rotating the spindle, amechanism for revolving the spindle and a mechanism for changing radiusof revolution can operate independently from one another, and a heavymember such as a motor is not rotated in a circular motion. This makesit possible to revolve the spindle at a higher speed and to freely set aratio of rotation number of the spindle to the revolution number of thesame accordingly and further to voluntarily change the revolution radiusof the spindle during its revolution.

With this balance adjustment, even when the revolution radius of thespindle is changed by rotating the eccentric shaft, the position of thecenter of gravity of the entire working apparatus does not changesubstantially. As a result, even when the revolution number of thespindle is increased, no vibration occurs. This makes it possible toincrease the revolution speed of the spindle, that is, the tool or theworkpiece without causing degradation in the working accuracy andincreasing the load on the tool.

According to the machining method of the invention, a ratio of therotation number of the tool or the workpiece to the revolution number isdetermined on the basis of the amount of working per unit time, that is,the working efficiency. Therefore, it is possible to set a rotationnumber and revolution number which have excellent working efficiencywithout shortening the life of the tool and increasing load on the tool.

According to another machining method of the invention, moreover, theratio of rotation number of the tool to the revolution number of thesame is set to a value below 37, so that a relative feed between thetool and the workpiece is increased in the intermittent cuttingoperation. As a result, cutting amount or working efficiency is notdecreased even if the cutting width per blade is reduced. In otherwords, as the cutting width per blade is reduced without degradation ofworking efficiency, heat generation, cutting resistance and impact forcecan be reduced, thereby improving the life of the tool. By increasingthe cutting amount per blade within the tool life, moreover, the workingefficiency can be improved.

According to another machining method of the invention, the ratio ofcutting speed established by the revolution of the tool or the workpieceis set to not less than 7%. As a result, the relative feeding speedbetween the tool and the workpiece is be increased, so that the loadapplied to the tool can be decreased according to the reduction of thecutting width per blade to improve the tool life and to improve theworking efficiency by increasing the cutting amount within the life ofthe tool.

In the still another machining method of the invention, therefore,various working operations such as rough work or finish work can beperformed by means of one apparatus or tool, resulting in the reductionin not only cost of installation but also in number of working steps toraise the working efficiency to a higher level.

According to still another machining method of the invention, when themachining operation is performed by moving the tool or the workpiecebackwards and forwards in the axial direction, the ratio of rotationnumber to revolution number is varied according to a relative movingdirection in the axial direction of the tool and the workpiece. Thismakes it possible to perform the rough work wherein the ratio ofrotation number to revolution number is decreased and the finish workwherein this ratio is increased, while the tool or the workpiece ismoved backwards and forwards in the axial direction. As a result, atotal working time can be shortened to improve the productivity.

INDUSTRIAL APPLICABILITY

The apparatus and method of the invention can be applied to variousmachining operations, specially, cutting operations or grindingoperations. Moreover, the proper setting of the ratio of the number ofrotation of the tool or the workpiece to the number of revolution of thetool or the workpiece enable the situations in which the tool and theworkpiece comes into contact with each other to be voluntarily changed.Therefore, this makes it possible to perform machining operations whichare excellent in the working efficiency or working accuracy, whereby ahigh availability of such an apparatus and method can be achieved in themachining industry.

What is claimed is:
 1. A machining apparatus for machining a workpieceby relatively rotating the workpiece and a tool, comprising: arevolution shaft held to rotate on an axis parallel to a center axis ofthe machining apparatus, a spindle rotating on an axis which is offsetwith respect to the center axis of the revolution shaft and parallel toa center axis of the revolution shaft and having a leading end on whichone of the workpiece and the tool is mounted, a rotation drivingmechanism for transmitting a power through a rotating member on a centeraxis of rotation of the revolution shaft or a member rotating integrallywith the revolution shaft to the spindle to rotate the same, whilerotating the revolution shaft and the spindle at different speedsrespectively.
 2. A machining apparatus according to claim 1, wherein therotation driving mechanism includes: a motor for revolution fixed on abase portion, a transmission mechanism for revolution for transmitting apower from the motor for revolution to the revolution shaft, a motor forthe spindle fixed on the base portion, and a transmission mechanism forthe spindle for transmitting a power from the motor for the spindle tothe spindle.
 3. A machining apparatus according to claim 2, wherein thetransmission mechanism for the spindle includes: a cylindrical memberenclosing an outer circumference of the spindle; a plurality of firstrollers fitted between the cylindrical member and the spindle so as torotate and revolve and rotatably held by the revolution shaft; an inputshaft inserted into the cylindrical member from an oposition side of thespindle and receiving a torque from the motor for the spindle; and aplurality of second rollers fitted between the input shaft and thecylindrical member so as to rotate and revolve and rotatably held by therevolution shaft.
 4. A machining apparatus according to claim 1, whereinthe revolution shaft includes an eccentric shaft rotating on an axisoffset with respect to the center axis of the revolution shaft, and thespindle is rotatably held in a position offset with respect to thecenter axis of the eccentric shaft.
 5. A machining apparatus accordingto claim 4, further comprising: a revolution radius varying mechanismfor rotating the eccentric shaft integrally with the revolution shaftand relatively with respect to the revolution shaft.
 6. A machiningapparatus according to claim 5, wherein the revolution radius changingmechanism includes a differential mechanism which performs adifferentiating rotation operation through three rotary elementsrotating relatively to one another, a first rotary element of the threerotary elements being connected to the transmission mechanism forrevolution, a second rotary element being connected to the eccentricshaft, and a third rotary element being connected to a revolution radiuschanging motor fixed on the base portion.
 7. A machining apparatusaccording to claim 4, wherein the spindle is balanced so that a centeraxis is aligned with the center of gravity; the eccentric shaft, onwhich the spindle is mounted in an offset position, is balanced so thata center axis is aligned with the center of gravity; and the revolutionshaft, on which the eccentric shaft is mounted with holding the spindlerotatably, is balance so that a center axis is aligned with the centerof gravity.
 8. A machining method for machining a workpiece by rotatingand revolving one of the workpiece and a tool and simultaneously bycontacting the one of the workpiece and the tool with the other of theworkpiece and the tool, comprising: determining an amount of machiningby the tool per unit time on the basis of at least one of apredetermined maximum machining sectional area and a predeterminedmachining speed, setting a ratio of a number of rotation of theworkpiece or the tool to a number of revolution of the workpiece or thetool on the basis of the amount of machining per unit time, andmachining the workpiece by rotating and revolving the workpiece or thetool so as to satisfy the ratio.
 9. A machining method for rotating andrevolving a tool having a cutting blade and intermittently cutting aworkpiece by means of the tool, wherein the workpiece is intermittentlycut by means of the cutting blade mounted on the tool by setting a ratioof a number of rotation of the tool to a number of revolution of thetool to a value below
 37. 10. A machining method for rotating andrevolving a tool having a cutting blade and intermittently cutting aworkpiece by means of the tool, wherein the workpiece is cut by settinga ratio of a cutting speed depending on a revolution of the tool, ascontained in a cutting speed of the cutting blade with respect to theworkpiece obtained when the tool is rotated and revolved, to not lessthan 7%.
 11. A machining method for machining a workpiece by rotatingand revolving one of the workpiece and a tool and simultaneouslycontacting the one of the workpiece and the tool with the other of theworkpiece and the tool, wherein the workpiece is cut by changing a ratioof a number of rotation of the one of the workpiece and the tool to anumber of revolution of the other of the workpiece and the tool on thebasis of a roughness produced on a machined surface of the workpiece.12. A machining method for machining a workpiece by rotating andrevolving one of the workpiece and a tool and simultaneously contactingthe one of the workpiece and the tool with the other of the workpieceand the tool, and moving the one of the workpiece and the tool backwardand forward in a direction parallel to a center axis of a rotation,wherein a ratio of a number of rotation to a number of revolution of theworkpiece or the tool is made different between a machining step ofmoving one of the workpiece or the tool forward in a direction parallelto the center axis of rotation and a machining step of moving one of theworkpiece or the tool backward in the direction parallel to the centeraxis of rotation.